1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device in which integrated circuits are formed on a semiconductor substrate containing a photoreceptor part, and more particularly relates to a method for manufacturing a semiconductor integrated circuit device in which opening parts are formed by etching inter-layer insulating films layered on a substrate.
2. Description of the Related Art
In recent years, optical disks such as CDs (compact disks) and DVDs (digital versatile disks) have come to occupy an important position as information recording media. Playback devices for such optical disks detect, using a light detector, the reflected light of the laser light with which the tracks of the optical disk are irradiated, and play back the recorded data on the basis of variations in the intensity of the reflected light.
FIG. 1 is a schematic plan view of a conventional light detector 10.
FIG. 2 is a schematic sectional view passing through the straight line A-A′ shown in FIG. 1, and showing the photoreceptor part 11 and wiring structures 12 in a sectional view perpendicular to the semiconductor substrate.
The light detector 10 has a photoreceptor part 11 containing PIN photodiode (PD) diffusion layers 34 divided into 4 segments in a 2×2 array on the surface of the semiconductor substrate 14A in order to detect reflected light. When reflected light of the laser light impinges on the photoreceptor part 11, a very weak photoelectric conversion signal is generated in the photoreceptor part 11. Such a light detector is disclosed in Japanese Laid-Open Patent Application No. 2001-60713. The generated signal is amplified by an amplifier formed in the surrounding area, and is input into an after-stage signal processing circuit.
Furthermore, the respective PD diffusion layers 34 are separated from each other by a separating diffusion layer 33.
The light detector 10 is manufactured by forming a gate oxide film 14B on the semiconductor substrate 14A, and successively layering a first interlayer insulating film 16, first metal layer 17, second interlayer insulating film 18, second metal layer 19, and third interlayer insulating film 20 on top of this. The first metal layer 17 and second metal layer 19 are respectively formed from aluminum (Al) or the like, and are patterned using a photolithographic technique. A wiring structure 12 and a signal line 13A and voltage application line 13B connected to the wiring structures 12 are formed by the patterned first metal layer 17.
The separating diffusion layer 33 is fixed in potential by the voltage application lines 13B via the wiring structures 12. The photoelectric conversion signals generated in the respective PD diffusion layers 34 are read out to the signal line 13A via the wiring structures 12.
In order to maintain the frequency characteristics of the photoelectric conversion signals and suppress the superimposition of noise onto the photoelectric conversion signals, it is necessary that the respective PD diffusion layers and signal lines 13A, and the separating diffusion layer 33 and voltage application lines 13B, all be electrically connected with a low resistance. Accordingly, the wiring structures 12 connected to the signal lines 13A and voltage application lines 13B are extended along the edges of the photoreceptor part 11 as shown in FIG. 1 in order to increase the size, and to form as many contacts as possible with the diffusion layers underneath. As a result, an area with a shape that has corner parts is defined on the photoreceptor part 11 by the wiring structures 12.
After the metal layers and inter-layer insulating films have been layered, the inter-layer insulating films and the like that are layered on top of the photoreceptor part 11 are etched and an opening part 15 is formed in order to increase the incident efficiency of light onto the photoreceptor part 11. The opening part 15 is formed with a shape that is similar to but much smaller than the shape surrounded by the wiring structures 12, and this opening part opens only at the surface of the photoreceptor part.
In order to increase the incident efficiency, it is necessary that the opening part 15 be etched as deeply as possible. When the inter-layer insulating film or the like is etched in order to form this opening part 15, the resist pattern 25 formed on the third inter-layer insulating film 20 is also etched from the surface. Accordingly, in cases where the film thickness of the resist is insufficient, the third inter-layer insulating film 20 underneath the resist is exposed by etching, and places that are not to be formed as the opening part are eaten away.
On the other hand, it is conceivable that the film thickness of the resist might be increased; however, if this occurs, the problem is still presented of a portion of the inter-layer insulating film or the like on the wiring structure 12 being etched.